Used in chemotherapy for the treatment of colorectal cancer, especially in advanced or metastatic cases. It is often part of first-line treatment regimens, typically combined with other drugs like fluorouracil and leucovorin. Works by inhibiting topoisomerase I, an enzyme involved in DNA replication, leading to DNA damage and cancer cell death. Also used in some cases of small cell lung cancer and other solid tumors when standard therapies are not effective. Administered intravenously under medical supervision due to its potent effects and potential side effects such as severe diarrhea and myelosuppression.